The present invention relates generally to the field of microstrip antennas, and more particularly to compact planar microstrip antennas.
Microstrip antennas are of lightweight, low profile, low cost and planar structure, replacing bulky antennas. The length of a rectangular microstrip antenna is about a half wavelength within the dielectric medium under the radiating patch, which is still relatively large at UHF and VHF frequencies, but these frequencies can impose size limitations resulting in bulky and cumbersome antenna structures.
Previously due to the size limitation at UHF and VHF frequencies, microstrip antennas were mainly limited to applications at higher frequencies. The disadvantage of size limitations in UHF and VHF has created a long-felt need to reduce antenna length. Up until now, it has not been possible to employ planar microstrip antennas without-the disadvantages, limitations and shortcomings associated with antenna length and size. The present invention males it possible to have electrically small planar microstrip antenna at low frequencies.
The need for electrically small planar microstrip antenna at low frequencies offers a number of advantages over prior art antennas. The compact planar microstrip antenna of the present invention provides the same high efficiency as conventional microstrip antennas. However, the present invention provides a key advantage over prior art antenna structures by requiring a substantially shorter antenna length, without suffering from the size limitations of prior art antenna structures. In one embodiment of the present invention, a reduced antenna length of at least 18% of the length of a conventional microstrip antenna has been achieved, resulting in small microstrip antennas at low frequencies such as UHF and VHF.
A prior art reference on conventional microstrip antennas is J. S. McLean, IEEE Trans, Antennas and Propagation, xe2x80x9cA Re-Examination of the Fundamental Limits on the Radiation Q of Electrically Small Antennaxe2x80x9d Vol. 44, pp 672-676, May 1996
The purpose of this invention is to introduce a compact planar microstrip antenna by reducing the antenna lengths to less than 18% of the length of a conventional microstrip antenna. Many military and commercial communication systems need compact, low-cost, rugged, and conformal antennas; as well as ground vehicle, aircraft and space antennas. In commercial systems, wireless communication systems need this antenna.
This invention provides the excellent properties of microstrip material (low cost, compact, planar and conformal) to design and fabricate electrically small planar microstrip UHF and VHF antennas.